Preheat the oven to 350 degrees F and line an 8-inch-square baking dish with foil, leaving an overhang; butter the foil. Whisk 2 cups flour, 1 teaspoon baking powder, and 1/2 teaspoon each baking soda and salt in a large bowl. In a separate large bowl, beat 1 stick room-temperature butter and 1 cup granulated sugar with a mixer on medium-high speed until light and fluffy, about 3 minutes. Add 2 eggs, one at a time, beating well after each addition. Beat in 2 teaspoons vanilla. Reduce the mixer speed to low and add the flour mixture in 3 batches, alternating with 1 cup sour cream total, beginning and ending with the flour mixture. The batter will be thick.

4. Choose a Filling

2/3 cup jam (any flavor)

2/3 cup chocolate-hazelnut spread

2/3 cup dulce de leche

2/3 cup apple butter

1 cup chocolate chips

1 1/2 cups fresh berries (or 1 cup thawed frozen berries)

5. Bake the Cake

Spread half of the batter in the prepared baking dish. Spread or sprinkle your filling on top in an even layer. Spoon the remaining batter over the filling and spread evenly. Sprinkle with the prepared topping. Bake until the topping is golden brown and a toothpick inserted into the center of the cake comes out clean, 55 minutes to 1 hour 5 minutes. Let cool 20 minutes in the baking dish, then lift out the cake using the foil and transfer to a rack to cool completely. Dust with confectioners' sugar, if desired.